1. Field of the Invention
The present invention relates to a process for producing wholly aromatic polyamide filaments heat-treated under tension. More particularly, the present invention relates to a process for producing wholly aromatic polyamide filaments heat-treated under tension without undesirable breakage of the individual filaments during the heat treating procedure under tension.
2. Description of the Prior Art
Recently, various industries need various types of synthetic filaments having highly improved properties, for example, a high tensile strength and modulus of elasticity. In order to reply to these needs, the fiber industry is attempting to develop and supply a new type of synthetic filaments having enhanced properties.
In the process for producing the new type of synthetic filaments, a certain type of filaments are subjected to a heat-treatment under tension, for instance, a drawing procedure at a high draw ratio at a high temperature, to enhance the properties thereof. Sometimes, the drawing and/or heat treatment procedures under tension result in undesirable adhesion of the individual filaments to each other. In other words, when a number of filaments in the form of a bundle are drawn and/or heat-treated under tension at an elevated temperature, they adhere to each other so that the resultant filament bundle exhibits a decreased usefulness, whereas each of the individual filaments exhibits improved properties.
For example, it is known that in order to obtain aromatic polyamide filaments having an excellent mechanical strength and modulus of elasticity, undrawn aromatic copolyamide filaments, as disclosed in British Patent No. 1,501,948, containing recurring units having a para-divalent aromatic radical and an ether radical as a copolymerized component, are drawn at a high draw ratio of 6.0 or more at a high temperature of 300.degree. C. or more. In the drawing procedures, the undrawn filaments are gradually stretched in a so-called flow drawing condition without the occurrence of necking.
However, in the flow drawing procedure at a high temperature, the undrawn filaments are significantly softened and adhere to each other. This adhering phenomenon is promoted with an increase in the number of individual filaments in the filament bundle and results in a decrease in the drawability of the filament bundle. Also, the resultant drawn filament bundle exhibits poor flexibility.
Japanese Unexamined Patent Publication (Kokai) No. 58-54021 (1983) discloses a method for preventing the undesirable adhesion of the individual filaments to each other in the drawing and/or heat-treatment procedures by applying an inorganic compound, for example, hydrated aluminum silicate, which method is capable of forming a hydrated gel onto peripheral surfaces of the filaments before the drawing procedures.
In the above-mentioned method, however, it was found by the inventors of the present invention that, when the method was applied to a filament bundle consisting of large number of individual filaments, the adhesion-preventing effect for the individual filaments was unsatisfactory. It was also found by the inventors of the present invention that the reasons for the above-mentioned unsatisfactory adhesion-preventing effect reside in the fact that when an aqueous dispersion of the hydrated gel-forming inorganic compound applied onto the peripheral surfaces of the filaments is dried, the decrease in the amount of water in the aqueous dispersion results in the deposition of inorganic compound particles, and then in the undesirable aggregation of the inorganic compound particles to form coarse particles on the peripheral surfaces of the filaments. The aggregation phenomenon results in uneven covering of the filament peripheral surface with the inorganic compound particles. The phenomenon of the uneven covering is promoted together with an increase in the number of individual flaments contained in the filament bundle.
Under the above-mentioned circumstances, it has been greatly desired to provide a new process for drawing a wholly aromatic filament bundle even at a high temperature and at a high draw ratio without adhesion of the individual filaments to each other.